Glass panes or panels form an important part of a building, contributing to aesthetics, weather-proofing and ambient light within the structure during the daytime.
In a conventional building structure, the building frame provides a mullion to which large glass panes or panels, often two or more panes overlaying one another and separated along their edges by spacers, are mounted using a sealant such as silicone to secure the panes in place. As is well known, the mullion has a raised channel extending generally centrally along the length of its front face, which channel may have ribbed internal side walls adapted to threadedly receive a screw. A window frame is formed by mullions that bound the four sides of the glass pane or panel known as a capped system, within the bounds of the raised channels. The windows are installed by applying a bead of silicone to the portions of the mullion faces ‘inside’ the channel, about the entirety of the mullion frame, and a glass pane or panel is mounted to the faces of the mullions to adhere to the silicone sealant. Sometimes a window frame may only have one, two or only three sides of exterior raised channels or pressure plates and the other sides simply installed with silicone sealant.
Once the glass panes or panels have been mounted to both sides of the mullion channel, a temporary holding block known as a pressure plate or “dutchy” is screwed to the mullion channel overlapping the side edges of the glass or panels which abut the front face of the mullion, typically using a self-tapping metal screw. The dutchies are maintained in position until the silicone has cured, at which point the dutchies are removed and a finishing trim or exterior silicone seal is applied to the front faces of the mullions, concealing the channel and the edges of the window pane.
Current techniques utilize a dutchy, typically formed from aluminium and often cut from excess pieces of trim that will be used to finish the mullions after the silicone has cured. There are a number of problems associated with this practice.
First, aluminium dutchies are created for use on the construction site. This requires time to cut the plate from a larger piece of trim and drill a hole in the right place, generally centrally along the length of the plate, and sometimes re-drill the hole if the initial hole is not positioned correctly. Then a tape or gasket is applied to the surface of the dutchy that will contact the glass or panel, to protect from direct contact to the finished surface. This involves some amount of labour, and once the dutchies are removed they become irrecoverable scrap and are discarded, so the time spent creating the dutchies is ultimately wasted, as are the materials.
Further, there is no gauge indicating how tightly to fasten the screw holding the dutchy in place. If the screw is over-tightened the glass pane can crack, requiring significant time and cost to replace.
In some cases the dutchy undergoes deformation due to over-tightening of the screw. This reduces the force applied by the dutchy to the glass pane, creating a risk of dislodgement of the glass pane or panel or its separation from the face of the mullion. In either case this diminishes the structural integrity of the window and potentially requires reinstallation or replacement of the glass pane or panel.
Applying the correct amount of torque to the screw to transfer sufficient force to the glass pane, so as to hold the glass pane in place during the curing cycle without cracking the glass, is often merely the result of fortuitous guesswork. Even where this is achieved, when an aluminium dutchy undergoes plastic deformation under a wind load after installation the dutchy will not return to its original profile and therefore loses some of its fastening strength, potentially leading to the problems identified above.
It would accordingly be beneficial to provide a dutchy which overcomes some or all of the aforesaid problems.